PHP session being cleared on one page

I have developed a theme in WordPress for an eCommerce website. The website makes use of sessions for the custom login system which I have created.

The issue is that one particular page, view basket, for some reason clears the session in FIREFOX when you view it.

I have this section of code in my functions file to start the session:

function init_sessions() {
if (!session_id()) {
    session_start();
}
}
add_action('init', 'init_sessions');

The following sessions are set when logging in:

$_SESSION['id']=$db['id'];
$_SESSION['timer']=time()+3600;
$_SESSION['remote_ip']=$_SERVER['REMOTE_ADDR'];

I tried removing the entire contents of the view basket script whilst leaving the print_r($_SESSION) in and it still got reset.

To replicate the view the website in FIREFOX: http://www.greengrocerschoice.co.uk

Login with email: test@bytewire.co.uk and password: password

Add a product or two to your basket then navigate to http://www.greengrocerschoice.co.uk/viewbasket/ when you reload the page having viewed this page you will notice that you are no longer logged in.

The following version of WordPress is being used: You are using WordPress 3.0.1.

Does anyone have any heads up on what might be causing the issues or tips to debugging to determine what is causing the issue?

Thanks